Abstract: A semiconductor device with an error detecting and displaying circuit included in the device for detecting whether or not a semiconductor unit within the device has a predetermined output according to a given input value, and for displaying the outputted results indicating an error state of the device. The error detecting and displaying circuit for a semiconductor unit having an input circuit, a logic processing circuit and an output circuit comprises an additional logic processing circuit connected to the semiconductor unit for logically operating logic signals sent from said semiconductor device. A comparison circuit is also connected both to the additional logic processing circuit and to the output circuit of said semiconductor unit for comparing signals from the additional logic processing circuit with signals from the output circuit to thereby output the compared results.