This invention relates to a heat conductive resin substrate which polybenzasol fibers are oriented in a thick direction and/or a direction of a surface of a resin substrate, further to the heat conductive resin substrate and a semiconductor package excellent in heat radiation ability which the semiconductor chips are mounted on the heat conductive resin substrate which the polybenzasol fibers are oriented in the thick direction (the Z direction) and/or the direction of the surface of the resin substrate, the heat conductive resin substance and the semiconductor package being provided with electrical insulation and high thermal conductivity, and being capable of controlling the thermal expansion coefficient.