The samples of cobalt monosilicide CoSi and its alloys with the substitution of iron or nickel for cobalt (Co$_1-x$M$_x$Si, M=Fe, Ni) were studied. The investigation were made for alloy compositions with iron content up to 10 at. % and nickel up to 5 at. %. The thermopower and electrical resistivity were measured in the temperature range of 100 – 800 K. Recent calculations of the cobalt monosilicide band structure revealed a number of essential differences from the standard semimetallic model with energy overlap of parabolic bands for electrons and holes. This raises the question on the effect of the new band structure features on the theoretical interpretation of experimental properties of the compound. We analyze the possibility of theoretical interpretation of temperature and concentration dependences of the thermopower and electrical resistivity using different models of the electron spectrum.