The intensity of a hot peppers is measured on the Scoville Scale, a system of measuring the Heat and spicyness of foods. The higher a peppers number on the scoville scale the more intense the flavor and heat. Guinness book of World Records lists the Carolina Reaper Pepper as the Worlds hottest pepper. In 2011 a Trinidad Scorpion Pepper was measured at 1.2 Million SHU.
If you are growing hot peppers and have trouble getting the intensity of sizzling masochistic flavor you'd like there are a number of tactics that can be employed to coax your plants to produce hotter peppers.
1. Full Sun, not partial shade but full sun is craved by hot peppers.
2. Water - you can probably grow many more peppers and even bigger peppers when your plants are well watered. However in order to produce a better quality pepper, you want the plant to be somewhat water stressed, particularly when bearing fruit. This forces the plant to produce a compound known as capsaicin which is what is responsible for the spicy heat of hot peppers.