A calorimetric miniaturized flow sensor was realized with a linear sensor response measured for water flow up to flow rates in the order of 300 nl min-1. A versatile technological concept is used to realize a sensor with a thermally isolated freely suspended silicon-rich silicon-nitride microchannel directly below the substrate surface. The microchannel concept allows for the planar integration of sensor structures in close proximity to the fluid, while chemical-resistant fluidic connections can be made directly on top of the microchannel, without introducing large dead-volumes. The realized flow sensor consists of a microchannel with low hydraulic resistance and 4.5 nl total fluid volume. A pressure driven flow setup was used to force water through the microchannel, measuring output sensitivity in the order of 0.2 μV/(nl min-1) for flows up to 300 nl min-1. The measured sensor output is in close agreement with results obtained from both a detailed and an approximate numerical model of the sensor.