A method of forming a micro pattern in a semiconductor device is disclosed. An oxide film mask is divided into a cell oxide film mask and a peri oxide film mask. Therefore, a connection between the cell and the peri region can be facilitated. A portion of a top surface of a first oxide film pattern between a region in which a word line will be formed and a region in which a select source line will be formed is removed. Accordingly, the space can be increased and program disturbance in the region in which the word line will be formed can be prevented. Furthermore, a pattern having a line of 50 nm and a space of 100 nm or a pattern having a line of 100 nm and a space of 50 nm, which exceeds the limitation of the ArF exposure equipment, can be formed using a pattern, which has a line of 100 nm and a space of 200 nm and therefore has a good process margin and a good critical dimension regularity.