A method for thermoplastic fusion bonding was introduced using a commercial pressure cooker as a thermal bonding chamber to apply heat and pressure for polymer thermal bonding. The chamber pressure was controlled by simply modifying the regulator weight, which decided the boiling point of water in the chamber. In this experiment, Poly-Methyl Methacrylate (PMMA) was thermally bonded using the proposed technique. For PMMA thermal bonding, 52 grams of regulator weight was well matched for 26.2 kPa of chamber pressure. The corresponding boiling temperature of water to the pressure was 105.5℃, which was the glass transitional temperature of PMMA. The thermal bonding system demonstrated bonding between the PMMA sheet and PMMA film without deformation of the microchannel. The bonding strength was characterized at 195.5±1 N.