X-ray spectrometers give the capability to determine chemical element composition in electron microscopes. The semiconductor with the most experience as an x-ray detector is silicon. Silicon is the most highly developed material on earth, and has a lot of good things going for it, but for some applications we crave something with other good properties. For example, for room temperature detectors it would be best to have a semiconductor with a wider band gap. For higher resolution it would be better to have a semiconductor with a smaller band gap. For these reasons a number of other semiconductors have been developed as x-ray detectors. In this article I will talk about narrow band gap semiconductors. Next time I will discuss large band gap semiconductors.