A micro reactor array for biochemical or biomedical use was developed. Conceptof this development is to get as much as biological data at the same time. Ninety-six micro reaction wells, volume of each well was 1.5 µl, were integrated in the array. The micro reactor array was fabricated on 1 mm thick silicon wafer and twelve pairs of a temperature sensor and a heater were formed on the backside. A tiny transparent window for optical measurement was formed at the center of bottom wall on each well. Several temperature gradients were applied to the array by means of few heaters and compared with simulation results to optimize the parameters. Finally, performance of the array was evaluated by basic DNA reaction. Advantages of the array system are the fast thermal response due to the small heat capacity and easy to make several reaction conditions in parallel.