The present invention provides an involatile memory device that is capable of data writing and erasing at a time other than during manufacturing, and a semiconductor device having the memory device. Also, the present invention provides a compact-sized and inexpensive involatile memory device and a semiconductor device having the memory device. A memory device of the present invention includes a first conductive layer and a second conductive layer of which at least one has a light transmitting property, and an organic compound layer that is in contact with the first conductive layer or the second conductive layer. The organic compound layer includes conductive particles that are dispersed within the layer, and the organic compound included in the organic compound layer has a site that can photoisomerize.