Abstract: A manufacturing method of a semiconductor integrated circuit device includes the steps of: providing wiring conductors capable of connecting between chips or devices and variable switching devices capable of connecting between predetermined wiring conductors on a wafer formed of a microcomputer built-in chip having a CPU and a writable memory circuit for storing an operation program or on a testing board provided with a microcomputer built-in device enclosed by a package; writing a testing program including the transmission and reception operation of signals between the devices or chips into the memory circuit re-writable and capable of using as a program storing area for one of the chips or devices; and executing the testing program in the CPU of the chip or device, thereby testing a testing chip, between the device and the testing chip or an input/output circuit of the device.