Abstract: A pattern generator for use in a semiconductor test device provided with a random access memory which has large capacity and runs at high speed and is capable of generating random pattern data having large capacity and running at high speed. Parts of random pattern data previously stored in a sequential pattern memory are transferred to addresses of a random pattern memory which are specified by the difference calculated by an arithmetic circuit between address data outputted from a control circuit and address data outputted from an address generator, and the transferred random pattern data are outputted to a semiconductor to be tested through a selection circuit.