A semiconductor device includes a first substrate on which an interface unit connectable to a host device is provided, a first memory module on the first substrate, and a first controller on the first substrate. The first controller includes a control unit that controls the first memory module, and a switching unit that switches an operation mode in response to a command from the host device. A first connecting portion is provided on the first substrate and is electrically connected to the first memory module and the first controller. The first controller can directly access a second memory module through the first connecting portion. Thus, for example the first controller can read data stored in the second memory module depending on operation mode.