The electrical properties of boron-doped (B-doped) diamond films prepared by microwave plasma chemical vapour deposition (CVD) were measured in the temperature range 77-900 K. The temperature dependence of the electrical resistivity rho was attributed to the activation energy epsilon(a) similar to 0.35 eV in the high temperature region and epsilon(l) similar to 0.05 eV in the low temperature region. The epsilon(h) value agreed well with the reported value for boron accepters in diamond. The transitional temperature T-t, at which the value of the activation energy changed from epsilon(l) to epsilon(n), decreased with increasing substrate temperature (T-S) during CVD diamond growth from 230 K at T-S=840 degrees C to 160 K at T-s=900 degrees C. An increase in the Hall mobility mu and reduction in the compensation ratio N-D/N-A were also observed with increasing substrate temperature. The piezoresistive properties of strain gauges composed of B-doped CVD diamond films were also investigated.