We describe new characterization methods that allow an accurate determination of all of the magnetic parameters that govern the behavior of magnetoresistive devices. These characterization methods are explained and used to measure the magnetic properties of MgO-based magnetic tunnel junction (MTJ) devices with magnetoresistance values of over 150%. We will show that the analysis of so-called “circle transfer curves,” which are measurements of the device magnetoresistance in a rotating, constant-magnitude applied field, can accurately determine the magnitude and direction of the free layer anisotropy as well as the pinned layer orientation and exchange bias strength. We also show how a measurement of the MTJ’s remnant resistance curve, obtained by saturating the MTJ at different field angles and then removing the applied field, can provide additional information on the free layer anisotropy characteristics. We will also compare our results with values extracted from traditional Stoner-Wohlfarth asteroid curves. Finally, we show that the extracted parameters can accurately predict the shape of traditional MTJ transfer curves.