Thank you for selecting Aerospace Aviation360 as your go-to distributor of part number MDS 21 found under Transistor by Freescale Semiconductor. The National Stock Number assigned to this part is 5961012416591, and the Federal Supply Class is 5961 Semiconductor Devices And Associated Hardware. Our website is owned and operated by ASAP Semiconductor, a leading distributor of aviation and aerospace part numbers like MDS 21.