Room temperature ohmic contacts to p- and n-type GaN using surface treatments were applied to the fabrication of GaN blue light emitting diode (LED). The state-of-the-art LED operation of the forward voltage of 3.1 V at the injection current of 20 mA was demonstrated without annealing processes. The surface treatment on p-type GaN using aqua regia solution caused the contact resistivity to decrease by three orders of magnitude. The inductively coupled plasma treatment on n-type GaN resulted in the contact resistivity of ~ 10E-6 ohm-cm2 at as-deposited state. Both treatments allowed the room temperature ohmic contacts to be realized on both substrates. Angle resolved synchrotron x-ray photoelectron spectroscopy was employed to examine the atomic composition at the treated surface. From this, the formation of ohmic contacts was deduced as due to the production of vacancies below the contact, that is, Ga vacancies for p-type contact and N vacancies for n-type one.