Abstract: A method of manufacturing a semiconductor integrated circuit device having a SOI structure includes the following steps. The first step is to form a semiconductor layer on a dielectric substrate. The second step is to form an oxide layer on the formed semiconductor layer. The third step is to form a nitride layer on the formed oxide layer. The fourth step is to remove a part of a plurality of layers composed of the semiconductor layer, the oxide layer, and a nitride layer so as to form a separated region in the layers. The fifth step is to coat a cooling agent on a surface of the nitride layer. The sixth step is to irradiate an energy beam from an outer surface of the cooling agent so as to monocrystallize the semiconductor layer. The seventh step is to remove the cooling agent from the surface of the nitride layer. And the final step is to oxidize a portion of the semiconductor layer located in the separated region by using the nitride layer.