We propose an algorithm based on singular value decomposition (SVD) to reduce the number of process variation variables. With few process variation variables, fault simulation and timing analysis under process variation can be performed efficiently. Our algorithm reduces the number of process variation variables while preserving the delay function with respect to process variation. Compared with the principal component analysis (PCA) method, our algorithm requires less computation time and guarantees the reduced process variation variables are independent. Experimental results on ISCAS85 circuits show that the algorithm works well. 1 INTROCUTION In modern multi-layer VLSI circuits, the dimension of the process variation is large. For example, in a k-metal technology, there are 2k variables for metal width and thickness, k variables for inter-layer dielectric (ILD) thickness, a gate length variable, and some other variables. With such a large number of process variation variables, timi...