A three dimensional (3D) transformer includes a first coil and a second coil. Each coil includes a first port, a second port, a top layer metal line, inter-layer inner metal lines, inter-layer outer metal lines and a bottom layer metal line. Each metal line of the first coil and that of the second coil are correspondingly arranged to the opposite side of each other. Each of the first port is electrically connected to each of the top metal line. Each coil is arranged clockwise from the top metal line, the inter layer inner metal line down to the bottom layer metal line and arranged clockwise from the bottom layer metal line, the inter layer outer metal line up to the upper metal line of the inter layer outer metal line. Each upper metal line of the inter layer outer metal line is electrically connected to each second port.