This paper reports a biochemical sensor for a label-free detection of cancer cell. A microcalorimeter has monitored the signal created from generated heat due to biochemical reaction between cancer cell and antibody in real time. HER2/neu receptor which is a remarkable biomarker of several cancers, especially breast cancer, was detected by using antibody, in this case HERCEPTIN®. In this study, the microcalorimeter was fabricated by using MEMS (Micro Electro Mechanical Systems)-technology. For higher sensitivity of microcalorimeter, it is important to reduce a parasitic heat transfer from a thermopile to a silicon substrate which has higher thermal conductivity (k = 148 W/m·K). Hot junctions of the proposed microcalorimeter are released from a silicon substrate by bulk micromachining to reduce loss of generated heat by reactions between biomolecules. NIH3T6.7 cell line with overexpressed HER2/neu receptor and FITC conjugated HERCEPTIN® were used. Each volume of biomolecules was 10 μl. HER2/neu receptor was detected by measuring output voltage change of the microcalorimeter about 7.92V/mole. For confirming a reliability of data, the measured data was compared with fluorescent data.