The micro fluidic chamber with narrow gap for high pressurized fluid has been designed and fabricated. The carbon dioxide (CO2) is injected into the narrow gap spaces of 0.5 μm and 1.6 μm. Their thermal resistance changes have been measured by changing the pressure and temperature. Hence, related to the effect of narrow space the critical pressure of supercritical CO2 is shifted to lower values. When the gap distance is shorter, the pressure of the minimum total-thermal-resistance (Rtotal) becomes lower. This 'narrow space effect' is enhanced by the shorter gap distance. Additionally, the change of thermal resistance related to pressure change is more responsive for narrower spacing. The smaller spacing seems to make more sensitive responsibility of the inserted fluid property. These results indicate that the filled fluid in a micro-chamber can be applied for the applications of sensing and switching devices using variable physical properties of the packaged fluid in narrow spaces.