A semiconductor device is disclosed which comprises a first wiring layer, a second wiring layer formed over the first wiring layer, data input/output terminals, and a data bus formed in the first and second wiring layers. The data bus includes N data lines transmitting data between a predetermined circuit and the input/output terminals. M first data lines among the N data lines have a length shorter than a predetermined length and residual N-M second data lines have a length longer than the predetermined length. Shield lines adjacent to the N data lines are formed in the first and second layers. The N data lines are arranged at positions at which the data lines do not overlap one another in a stacking direction of the first and second wiring layers.