The present invention relates to a millimeter-wave transmitter on a chip comprising at least one transmit path coupleable to an oscillator, and an on-chip power sensor to measure at least a portion of a transmit power transmitted over the at least one transmit path. The present invention further relates to a method of calibrating a millimeter-wave transmitter on a chip and an on-chip power sensor coupleable to at least one transmit path of a millimeter-wave transmitter. The embodiments of the present invention provide a direct measure of transmit power provided within an individual one of the transmit paths of the millimeter-wave transmitter.