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In order to investigate Marangoni flow instability of molten silicon, surface oscillation of a silicon liquid bridge with various aspect ratios at high Marangoni numbers, such as Ma ≥ 2400, was observed by using real-time phase-shift interferometry. By analyzing phase distribution of the phase-shift interferograms using FFT (fast Fourier transformation) and wavelet transformation, we found that two frequency bands exist in surface oscillation. Their central frequencies are 0.1–0.5 Hz for a lower band and 0.7–1.3 Hz for a higher band, respectively. Central frequency decreases with increase in aspect ratio. The lower frequency bands, which include m = 1 and m = 3 modes, appear continuously, whereas the higher frequency bands appear intermittently.