Extensive surveys of both the near and far noise fields were made for a supersonic (nozzle design Mach number 1.5) cold model jet. The operating conditions selected for this investigation were (1) shock‐free mode at operating pressure ratio (reservoir pressure/ambient pressure), ξ=3.57 and (2) underexpanded mode at ξ=4.74. The experiments were conducted in a fully anechoic chamber. The purpose of this investigation was to extend the existing understanding of the noise field of a supersonic shock‐free jet at a moderate exit Mach number and the variations in its acoustic behavior when the nozzle was operated at underexpanded mode where strong shock waves were present. The main experimental results obtained are presented. It was found that the broad‐band and sound‐pressure spectra of apparent sources in each of the individual characteristic flow regions were similar. The strongest source for the shock‐free jet was located near the laminar core tip, whereas for underexpanded jet, the strongest source was found near the middle of the flow region containing shock waves. It is shown that the significant increase in the noise output at the underexpanded mode of operation was primarily contributed by high‐frequency components.