This paper presents a characterization of the modulation bandwidth in high-frequency voltage-controlled oscillators (VCOs) fabricated using 130 nm SiGe BiCMOS technology. The study focuses on analyzing the modulation bandwidth’s dependency on key parameters such as tuning sensitivity, oscillation frequency, and amplitude of the modulating signal for LC cross-coupled oscillators with MOS-varactors for frequency adjustment. Experimental investigations demonstrate the conditions under which the modulation bandwidth can be approximated by the frequency deviation (∆f). The results highlight the complex interplay between VCO’s tuning sensitivity (KVCO), modulation frequency, and linearity, shedding light on the factors influencing the modulation bandwidth’s behavior. The findings provide valuable insights for the design and optimization of VCOs in high-frequency applications, particularly in radar systems, communication circuits, and frequency synthesizers employed in frequency-modulated continuous-wave (FMCW) radar setups.