A data transfer method is disclosed in a multi-chip semiconductor device which comprises a plurality of inter-chip wires. First, a test is conducted to determine whether or not each inter-chip wire is capable of normally transferring data, on circuits arranged on chips between which the inter-chip wire is connected. When an inter-chip wire incapable of normally transferring data exists, the data transfer speed of the buffer circuit that is on the chip on the transmission and that is connected to an inter-chip wire capable of normally transferring data is increased. The buffer circuit, whose data transfer speed has been increased, transfers data which would otherwise be transferred through the inter-chip wire incapable of normally transferring data, together with the data which should be transferred thereby, to the chip on the reception side chip through an inter-chip wire connected to the buffer circuit at the data transfer speed.