A tamper-resistant semiconductor device (5;20;30;40;50;60) which includes a plurality of electronic circuits formed on a circuitry side (6) of a substrate (7) having an opposite side which is a backside (8) of the semiconductor device, and comprises at least one light-emitting device (9a-f;21) and at least one light-sensing device (10a-f;22a-b) provided on the circuitry side (6) of the semiconductor device. The light-emitting device (9a-f;21) is arranged to emit light, including a wavelength range for which the substrate (7) is transparent, into the substrate towards the backside (8), and the light-sensing device (10a-f;22a-b) is arranged to sense at least a fraction of the emitted light following passage through the substrate (7) and reflection at the backside (8), and configured to output a signal indicative of a reflecting state of the backside, thereby enabling detection of an attempt to tamper with the backside (8) of the semiconductor device (5;20;30;40;50;60). Through the present invention, a semiconductor device can be equipped with a backside tamper protection which neither restricts the field of application of the semiconductor device, nor the choice of packaging of the device.