The present invention provides a semiconductor device which enables data compression with a small amount of data. The present invention is a semiconductor device which includes a pixel portion, a memory, a first circuit, and a second circuit. The pixel portion has a function of obtaining imaging data. The first circuit has a function of performing discrete cosine transform on the imaging data, and generating first data. The first data is analog data, and the memory has a function of retaining the first data. The second circuit has a function of performing discrete cosine transform on the first data, and generating second data. The memory includes a first transistor, which includes an oxide semiconductor in a channel formation region, and a second transistor, in which a channel formation region is provided in a Si wafer.