The pepper commonly used in very spicy salsas with a Scoville rating above 100,000 is the habanero.
Habaneros are chili peppers in the species Capsicum chinense, prized for intense heat, fruity aroma and a distinctive citrus-like flavor. Typical habaneros are often rated around 100,000–350,000 Scoville heat units (SHU), although the exact heat varies with cultivar, growing conditions and the individual fruit.
They are especially common in fiery Mexican and Caribbean sauces. A small amount can dominate a salsa, so cooks often balance the pepper with citrus, fruit, tomato, onion or vinegar. Habanero heat also tends to build over several minutes and may linger for a long time.
The alternatives are generally milder: serranos are commonly around 10,000–25,000 SHU, jalapeños around 2,500–10,000, and poblanos around 1,000–2,500. Habaneros are no longer the world’s hottest peppers; varieties such as the Carolina Reaper and Pepper X are substantially hotter.