A new tunable integrated transformer topology together with its tuning method is presented. The proposed tunable topology consists of a conventional tapped transformer and a coupled inductor. The phase shift between the input power into the primary winding and that into the coupled inductor was used to control the electrical characteristics such as maximum stable gain, input impedance and quality factor. The new tunable transformer achieved about 3dB higher maximum stable gain and 2.8 times higher quality factor compared to the conventional transformer.