High-mass stars have a mass several times that of the sun. These stars are less numerous in the universe because clouds of gas tend to condense into many smaller stars. Furthermore, they have shorter lifespans than low-mass stars. Despite their reduced numbers, these stars still have some very distinguishing and noticeable characteristics.

All stars are powered by nuclear fusion at their core. A star spends most of its life in a phase known as the main sequence, in which its fuses hydrogen atoms into helium. A high-mass star will have more hydrogen to burn in this process. The energy released by this process will maintain higher temperatures and the star will, in turn, burn more hydrogen than a low-mass star. Hence, high-mass stars burn out their energy quicker than low-mass stars. A star with a mass ten times that of the sun can live on the main sequence of 20 million years, whereas low-mass stars, such as red dwarf stars, may have main-sequence lifespans greater than the current age of the universe.

Stars are divided into different classes according to their spectral characteristics. The main spectral classes, in order of decreasing temperature, are O, B, A, F, G, K and M. These classes also correspond to the mass of stars, with O-class stars being the most massive. The sun is a G-class star. M-class stars have a mass of roughly 10 percent of the sun's and have a surface temperature between 2,500 to 3,900 K. By contrast, O-class stars can have a mass 60 times greater than the sun's and have surface temperatures ranging from 30,000 to 50,000 K. Spectral class B includes stars with masses around two or three times the mass of the sun to around 18 times the mass of the sun. The temperature of B-class stars ranges from 11,000 to 30,000 K. Spectral classes A and F include stars that are only slightly more massive than the sun.

Stars that are at least 1.3 times as massive as the sun can undergo a different type of fusion than that seen in most other stars. Less massive stars undergo hydrogen fusion during their main sequence life and helium fusion in their later life. More massive stars can create helium through both hydrogen fusion as well as the carbon-nitrogen-oxygen process. This allows these stars to continue to burn even after all of the hydrogen and helium has been used up. In turn, these high-mass stars can fuse increasingly large elements in their later life.

At the end of a high-mass star's life, its core is made up of iron. This iron is stable, and will not undergo fusion. Eventually, the iron core collapses due to gravity, and the star can explode as a supernova. Depending on the star's mass, the core of the star can become a neutron star or a black hole. These endpoints are very different from a majority of other stars, which end their lives as hotter white dwarf stars.