This paper investigates 1/f noise behavior under low and high drain biases of high-voltage metal-oxide-semiconductor field-effect transistors (MOSFETs) (HV-MOSFETs). A dedicated setup is presented which allows measuring low-frequency (LF) noise of lateral double-diffused MOSFETs (LDMOSFETs) up to 200 V at the drain. LF noise spectra of n- and p-channel LDMOSFETs were measured over a large range of gate and drain bias conditions and modeled using a recently established physics-based compact model of HV-MOSFETs. The investigated devices confirm that the overall noise is mostly dominated by the noise originating in the channel, while the drift-region-generated noise only is apparent in linear operation.