We have investigated temperature and electron-numebr (band-filling) dependence of Seebeck coefficient in B20-type transition-metal monosilicides experimentally to gain the systematics of thermoelectric properties. This can lead to a perspective on the materials design of metallic thermoelectric compounds by comparing a result of band calculation. On the basis of the seebeck coefficient measurement, we show the global systematics of thermopower for a wide range of materials (CrSi - MnSi - FeSi - CoSi - Co0.85Ni 0.15Si and their interpolating solid solutions). Versatile behaviors of Seebeck coefficient are observed with variations of temperature and electron-number: steep or gradual sign change, a large positive or negative value of Seebeck coefficient, etc. As for the thermoelectricity in these materials, the best performance among these materials is around CoSi at room temperature, showing large adjacent p- and n-type thermopower. The power factor (S2/ρ) is evaluated 25 μW/cmK2 at CoSi, which is as high as that of Na0.75CoO2 a material known for a thermoelectric oxide material, though the thermal conductivity is larger (-10 W/mK).