A miniaturized multilayer hybrid-phase signal splitter circuit is proposed, which is fully equivalent in function to a conventional rat-race coupler, but with a specialized circuit layout structure that allows its IC implementation to be more miniaturized than the conventional rat-race coupler. The proposed hybrid-phase signal splitter circuit features the use of a multilayer substrate for the layout of six transmission lines in such a manner that the transmission lines in the middle layer are inductively coupled to the transmission lines on the overlying layer as well as the transmission lines on the underlying layer to form a Marchand balun. In IC implementation, the required layout area is only about 10% of the layout area for the conventional rat-race coupler.