The perylene (C20H12) layer effect on the electrical and dielectric properties of Al/p-Si (MS) and Al/perylene/p-Si (MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz-2 MHz. Experimental results show that C-V characteristics give an anomalous peak for two structures at low frequencies due to interface states (N-ss) and series resistance (R-s). The increases in C and G/omega at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant (epsilon') and dielectric loss (epsilon '') are subtracted using C and G/omega data at 1.5 V. The epsilon' and epsilon '' values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(sigma(ac))-ln(omega) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C-2-V characteristics, the doping acceptor atom concentration (N-A) and barrier height (Phi(B)) for Schottky barrier diodes (SBDs) of MS and MPS types are also obtained to be 1.484 X 10(15) and 1.303 x 10(15) cm(-3), and 1.10 and 1.13 eV, respectively.