Bus/memory bandwidth consumption caused by reading of auxiliary information not included in compressed data is reduced. A memory stores compressed data and auxiliary information used to read the compressed data. A semiconductor device includes a cache in which auxiliary information stored in the memory is stored, a control unit which, when a read request for reading compressed data stored in the memory is received, reads from the cache auxiliary information about the compressed data, if stored in the cache, or reads the auxiliary information about the compressed data, if not stored in the cache, from the memory and stores the auxiliary information about the compressed data in the cache, and which reads the compressed data from the memory using the auxiliary information about the compressed data, and an expansion unit to expand the compressed data read from the memory.