相变化内存（英语：Phase-change memory，英语：Ovonic Unified Memory，英语：Chalcogenide RAM，简称PCM, PRAM, PCRAM, CRAM），又译为相变位内存，是一种非易失性存储器设备。PRAM 使用含一种或多种硫族化物的玻璃（Chalcogenide glass）制成。硫族化物玻璃的特性是，经加热可以改变它的状态，成为晶体（Crystalline）或非晶体（Amorphous）。这些不同状态具有相应的电阻值。因此 PRAM 可以用来存储不同的数值。 它是可能取代闪存的技术之一。

Phase-change memory (also known as PCM, PCME, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type of non-volatile random-access memory. PRAMs exploit the unique behaviour of chalcogenide glass. In the older generation of PCM heat produced by the passage of an electric current through a heating element generally made of TiN would be used to either quickly heat and quench the glass, making it amorphous, or to hold it in its crystallization temperature range for some time, thereby switching it to a crystalline state. PCM also has the ability to achieve a number of distinct intermediary states, thereby having the ability to hold multiple bits in a single cell, but the difficulties in programming cells in this way has prevented these capabilities from being implemented in other technologies (most notably flash memory) with the same capability. Newer PCM technology has been trending in two different directions. One group have been directing a lot of research towards attempting to find viable material alternatives to Ge₂Sb₂Te₅ (GST), with mixed success. Another have developed the use of a GeTe - Sb₂Te₃ superlattice to achieve non-thermal phase changes by simply changing the co-ordination state of the Germanium atoms with a laser pulse. This new Interfacial Phase Change Memory (IPCM) has had many successes and continues to be the site of much active research.