A semiconductor device in which unwanted change in the secondary data which must be reliable is suppressed and the need for a considerable increase in the capacity of a memory unit can be avoided. Also it ensures efficient data processing by asymmetric access to the memory unit. It includes a memory unit having a first memory without an error correcting function, a second memory with an error correcting function, and a plurality of access nodes for the memories. A plurality of buses is coupled to the access nodes and a plurality of data processing modules can asymmetrically access the memory unit through the buses. The first memory stores primary data before data processing by the data processing modules, and the second memory stores secondary data after data processing by the data processing modules.