Methods of forming semiconductor devices including optical devices

It provides a method for forming a semiconductor device including the optical element. According to this method, the first in preparing a semiconductor substrate including a first region and a second region, but forming a first buried oxide film in the semiconductor substrate of the first region, first phase buried oxide film and the first region 1 the semiconductor layer is defined. Forming a trench in a semiconductor substrate of the second area to define the active portion, forming a capping semiconductor pattern on the upper part and the upper surface of the active parts of the side wall. At this time, to expose the bottom of the active parts of the side wall. Performing an oxidation process to oxidize the active parts of the bottom of the capping and the semiconductor pattern to form an oxide film. First to form a first optical element to the semiconductor layer. Non-oxidized portion and the active portion is the core of the optical signal passes through, one end of the core is connected to the first optical element.