On 26 February 1999 Intel released the Pentium III processor. The first Pentium III was based on the Katmai core. An evolution of the Pentium II Deschutes. Notable differences can be found in the addition of SSE instructions and an improved L1 cache controller. The Pentium III was released in 450MHz and 500MHz versions with later increments to 550MHz and 600MHz. In Q3 of 1999 Intel also released 533B and 600B models with an 133MHz FSB.

Katmai still has off-die L2 cache like the Pentium II but with a slightly difference plastic CPU packaging for better cooling.