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We report on the first measurement of the liquid flow rate utilizing the variation in junction voltage across a laser due to the self-mixing effect. A packaged single-mode VCSEL with integrated photodiode is used as the self-mixing sensor. Signal was acquired from both the photodiode and the laser junction voltage. With appropriate signal processing, both detection methods produced comparable results despite voltage signal exhibiting marginally lower signal-to-noise ratio. The voltage detection scheme leads to a more compact and reduced-cost measuring system eliminating the need for the monitoring photodiode and will have significant manufacturing advantages in the future applications based on two-dimensional VCSEL sensor arrays.