The BT139B-800G.118 is a Thyristor manufactured by WeEn Semiconductor. It is a low-cost, high-sensitivity bidirectional triggering thyristor. The thyristor has a reverse voltage rating of 800V, an on-state current rating of 17A, and a maximum junction temperature rating of 150°C. The part is designed for applications such as motor speed control, electronic thermostats, and overvoltage protection.