A semiconductor module having a built-in antenna element for use in a system of a band of millimeter-waves or quasi-millimeter-waves comprises a substrate, an antenna element, a semiconductor integrated circuit, and a hermetically sealing portion. The antenna element is mounted on one side of the substrate. The semiconductor integrated circuit is also formed on the same side of the substrate as of the antenna element. The semiconductor integrated circuit includes at least either of a transmitter signal processing circuit composed mainly of an amplifier circuit and a frequency converter circuit for processing a signal which is exploited in the system of the band of millimeter-waves or quasi-millimeter-waves and transmitted to the antenna element, and a receiver signal processing circuit composed mainly of an amplifier circuit and a frequency converter circuit for processing a signal which is received by the antenna element and exploited in the system of the band of millimeter-waves or quasi-millimeter-waves. The hermetically sealing portion is designed for hermetically sealing the antenna element and the semiconductor integrated circuit formed on the substrate within a common space defined by a boundary surface or the side of the substrate while the transmissivity of radio waves to the antenna element for the system of the band of millimeter-waves or quasi-millimeter-waves is maintained.