Structural and electronic properties of RuSi, RuGe and OsSi are investigated by first-principle density-functionalcalculations based on ultrasoft pseudopotential and generalized gradient approximations for the exchange-correlation functional The bulk moduli for RuGe and OsSi which have not been available from experiments are predicted to be 2.08 and 2.65 Mbar. Though all these compounds with a B20 structure are semiconductors according to the calculation, their band gaps are overestimated compared to those from experiments by a factor of about two.