An on-chip antenna includes an integrated circuit chip, a reflective conductor, at least one first coupler, at least one patch antenna element, a connection, and at least one second coupler. The integrated circuit chip includes a semiconductor, has an active surface and a back surface opposed to each other, and has a semiconductor circuit. The reflective conductor is disposed above the back surface. The at least one first coupler is disposed between the back surface and the reflective conductor. The at least one patch antenna element is disposed above the reflective conductor. The connection couples the at least one patch antenna element and the at least one first coupler. The at least one second coupler is provided on the active surface to be electrically conductive to the semiconductor circuit, and is opposed to the at least one first coupler and in non-contact with the at least one first coupler.