A method of forming a non-volatile memory having a floating trap-type device is disclosed in the present invention. In the method, a relatively thick thermal oxide layer is formed at a semiconductor substrate and patterned to leave a thick thermal oxide pattern at a high-voltage region (a high-voltage region defining step). An oxide-nitride-oxide (ONO) layer is formed over substantially the entire surface (the substantial surface) of the semiconductor substrate and patterned to leave an ONO pattern at a cell memory region (a cell memory region defining step). After the high-voltage region defining step and the cell memory region defining step, a thermal oxidizing process is performed with respect to the semiconductor substrate where a low-voltage region is exposed, thereby forming a relatively thin gate insulation layer for a low-voltage type device (a low-voltage region defining region).