Abstract: The present invention relates to a process for the preparation of a boron phosphide, more specifically BP and/or B12P2, comprising the mechanochemical reaction of boron phosphate (BPO4) with at least one alkaline earth metal (EA). In particular, the process of the invention allows for the selective preparation of either BP or B12P2 with more than 95% purity, through the reduction of boron phosphate (BPO4) with at least one alkaline earth metal (EA) according to reaction (1) for BP and according to reaction (2) for B12P2: BPO4+4 EA?BP+4 EA(O) (1) 2BPO4+5 (EA)B2+3 EA?B12P2+8 EA(O) (2). The present invention further relates to boron phosphide powders, in particular BP or B12P2 powders, of nanometric or micrometric size.