A compact quantum random number generator based on the measurement of the arrival time of photons is presented in this paper. The new system consists of a silicon nanocrystals light emitting device coupled with a SPAD-based detector, integrated in a 3D chip packaging. The miniaturization of the device allows a remarkable reduction of the system size with respect the state of the art. The detector consists of an array of 16 pixels connected to a cluster of 4 reconfigurable TDCs with 12 bit resolution each for photon time stamping. Maximum system bit rate, limited by the emission efficiency of the source, is 0.4 Mbps.