Method for calculation of cell delay time and method for layout optimization of semiconductor integrated circuit

In a circuit simulation step, a cell transistor level net list is input, the slew of an input signal waveform and the magnitude of a load capacitance connected to a cell output terminal are varied for each cell, to perform a circuit simulation of each cell for obtaining an output signal waveform. Next, in a dependence table generation step, the dependence of the output signal waveform slew upon the input slew rate and the load capacitance is calculated for each cell, the dependence thus calculated is compared with a predetermined threshold level, and according to the dependence level, a delay calculation expression with consideration taken to the delay of signal propagation between the cell input and output terminals and another without such consideration are selectively used. Accordingly, the delay times of the cells forming a semiconductor integrated circuit can be calculated at high accuracy and at high processing speed.