下加利福尼亚半岛（西班牙语：Península de Baja California）位于墨西哥西部，从北端的蒂华纳到南端的圣卢卡角，全长1250公里，把太平洋与加利福尼亚湾分隔开来，政治上分为下加利福尼亚州和南下加利福尼亚州。

The Baja Cali Peninsula (English: Lower California Peninsula, Spanish:Península de Baja California) is a peninsula in Northwestern Mexico. Its land mass separates the Pacific Ocean from the Gulf of California. The peninsula extends 1,247 kilometres (775 mi) from Mexicali, Baja California in the north to Cabo San Lucas, Baja California Sur in the south. It ranges for 40 kilometres (25 mi) at its narrowest to 320 kilometres (200 mi) at its widest point and has approximately 3,000 kilometres (1,900 mi) of coastline and approximately 65 islands. The total area of the Baja California Peninsula is 143,390 square kilometres (55,360 sq mi).