A semiconductor device includes external interface terminals and processing circuits, and it is fed with an operating power source when detachably set in a host equipment. Power source feeding terminals (VCC, VSS) among the external interface terminals are long enough to keep touching the corresponding terminals of the host equipment for, at least, a predetermined time period since the separation of an extraction detecting terminal among the external interface terminals, from the corresponding terminal of the host equipment, and they are formed to be longer in the extraction direction of the semiconductor device than the extraction detecting terminal. Thus, a time period till the cutoff of the power source is easily made comparatively long. The power source feeding terminals should preferably be extended onto the insertion side of the semiconductor device, but an extendible distance is sometimes liable to be limited. In order to ensure the necessary time period without changing the length and shape of the power source feeding terminals on the semiconductor device side, each of the power source feeding terminals may be formed so as to have two, front and rear touch points with the corresponding connector terminal of the host equipment side, but complicated improvements are necessitated for the construction of the connector terminal of the host equipment side. According to the semiconductor device, the time period required till the power source cutoff is easily ensured, and the complicated improvements are not required for the construction of the corresponding connector terminals of the host equipment side.