Hi, I have Ids vs Vds characteristic curves for a MOSFET at Vgs = 2V and Vgs = 2.5V in both the linear (ohmic) and saturated regions. I wanted to try to figure out the threshold voltage for the MOSFET from this information only. I had two ideas of how to do this, but they differ by a factor of 2. I want to know why the estimates are so different from each other. Idea 1: From the characteristic curves, I know that in the saturation region, Ids' = 1.4mA @ Vgs' = 2.5V and Ids = 0.65mA @ Vgs = 2V. Use, Ids'/Ids = (Vgs'-Vt)^2/(Vgs-Vt)^2 => 2 = (2.5-Vt)^2/(2-Vt)^2 Solving for Vt, I get Vt = 0.8V, 2.2V. I neglect 2.2V because Vds > Vgs - Vt in the saturation region Idea 2: Use the Vds of the "knee" (where the curves turn over in transitioning between the linear region and the saturation region) as the the saturation voltage of Vds, and use the condition Vds_sat = Vgs - Vt. On the Vgs = 2V curve, this knee occurs near Vds = 0.5V, which means Vt = 1.5V, fairly different from the 0.8 volt guess I got above. Similarly, on the Vgs = 2.5V curve, the knee occurs near Vds = 0.7V, which means Vt = 1.8V The 1.5V and 1.8V threshold voltage estimates from method 2 are pretty similar (especially since I am eyeballing the knee for the curve) but these differ a lot from 0.8V from method 1. Why?