diff --git a/docs/changelog.rst b/docs/changelog.rst
index c60bbf09..1dcbfb51 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -4,7 +4,7 @@ Changelog
 
 Development
 ===========
-- (Fill this out as you fix issues and develop your features).
+- Improve performances by removing SemiStrictDict
 
 Changes in 0.14.0
 =================
diff --git a/mongoengine/base/datastructures.py b/mongoengine/base/datastructures.py
index b9aca8fa..cd6ac641 100644
--- a/mongoengine/base/datastructures.py
+++ b/mongoengine/base/datastructures.py
@@ -445,42 +445,3 @@ class StrictDict(object):
 
             cls._classes[allowed_keys] = SpecificStrictDict
         return cls._classes[allowed_keys]
-
-
-class SemiStrictDict(StrictDict):
-    __slots__ = ('_extras', )
-    _classes = {}
-
-    def __getattr__(self, attr):
-        try:
-            super(SemiStrictDict, self).__getattr__(attr)
-        except AttributeError:
-            try:
-                return self.__getattribute__('_extras')[attr]
-            except KeyError as e:
-                raise AttributeError(e)
-
-    def __setattr__(self, attr, value):
-        try:
-            super(SemiStrictDict, self).__setattr__(attr, value)
-        except AttributeError:
-            try:
-                self._extras[attr] = value
-            except AttributeError:
-                self._extras = {attr: value}
-
-    def __delattr__(self, attr):
-        try:
-            super(SemiStrictDict, self).__delattr__(attr)
-        except AttributeError:
-            try:
-                del self._extras[attr]
-            except KeyError as e:
-                raise AttributeError(e)
-
-    def __iter__(self):
-        try:
-            extras_iter = iter(self.__getattribute__('_extras'))
-        except AttributeError:
-            extras_iter = ()
-        return itertools.chain(super(SemiStrictDict, self).__iter__(), extras_iter)
diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index d05c7695..f8ab73d0 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -13,7 +13,7 @@ from mongoengine import signals
 from mongoengine.base.common import get_document
 from mongoengine.base.datastructures import (BaseDict, BaseList,
                                              EmbeddedDocumentList,
-                                             SemiStrictDict, StrictDict)
+                                             StrictDict)
 from mongoengine.base.fields import ComplexBaseField
 from mongoengine.common import _import_class
 from mongoengine.errors import (FieldDoesNotExist, InvalidDocumentError,
@@ -79,8 +79,7 @@ class BaseDocument(object):
         if self.STRICT and not self._dynamic:
             self._data = StrictDict.create(allowed_keys=self._fields_ordered)()
         else:
-            self._data = SemiStrictDict.create(
-                allowed_keys=self._fields_ordered)()
+            self._data = {}
 
         self._dynamic_fields = SON()
 
diff --git a/tests/test_datastructures.py b/tests/test_datastructures.py
index 6830a188..79381c5a 100644
--- a/tests/test_datastructures.py
+++ b/tests/test_datastructures.py
@@ -1,6 +1,6 @@
 import unittest
 
-from mongoengine.base.datastructures import StrictDict, SemiStrictDict
+from mongoengine.base.datastructures import StrictDict
 
 
 class TestStrictDict(unittest.TestCase):
@@ -76,44 +76,5 @@ class TestStrictDict(unittest.TestCase):
         assert dict(**d) == {'a': 1, 'b': 2}
 
 
-class TestSemiSrictDict(TestStrictDict):
-    def strict_dict_class(self, *args, **kwargs):
-        return SemiStrictDict.create(*args, **kwargs)
-
-    def test_init_fails_on_nonexisting_attrs(self):
-        # disable irrelevant test
-        pass
-
-    def test_setattr_raises_on_nonexisting_attr(self):
-        # disable irrelevant test
-        pass
-
-    def test_setattr_getattr_nonexisting_attr_succeeds(self):
-        d = self.dtype()
-        d.x = 1
-        self.assertEqual(d.x, 1)
-
-    def test_init_succeeds_with_nonexisting_attrs(self):
-        d = self.dtype(a=1, b=1, c=1, x=2)
-        self.assertEqual((d.a, d.b, d.c, d.x), (1, 1, 1, 2))
-
-    def test_iter_with_nonexisting_attrs(self):
-        d = self.dtype(a=1, b=1, c=1, x=2)
-        self.assertEqual(list(d), ['a', 'b', 'c', 'x'])
-
-    def test_iteritems_with_nonexisting_attrs(self):
-        d = self.dtype(a=1, b=1, c=1, x=2)
-        self.assertEqual(list(d.iteritems()), [('a', 1), ('b', 1), ('c', 1), ('x', 2)])
-
-    def tets_cmp_with_strict_dicts(self):
-        d = self.dtype(a=1, b=1, c=1)
-        dd = StrictDict.create(("a", "b", "c"))(a=1, b=1, c=1)
-        self.assertEqual(d, dd)
-
-    def test_cmp_with_strict_dict_with_nonexisting_attrs(self):
-        d = self.dtype(a=1, b=1, c=1, x=2)
-        dd = StrictDict.create(("a", "b", "c", "x"))(a=1, b=1, c=1, x=2)
-        self.assertEqual(d, dd)
-
 if __name__ == '__main__':
     unittest.main()