  Anisotropic thermal transport plays a key role in both theoretical study and
engineering practice of heat transfer, but accurately measuring anisotropic
thermal conductivity remains a significant challenge. To address this issue, we
propose the three-sensor 2{\omega} method in this study, which is capable of
accurately measuring the isotropic or anisotropic thermal conductivity of solid
materials. In this method, several three-sensor groups following the design
guidelines are fabricated upon the sample along different characteristic
directions, and each group consists of three parallel metal sensors with
unequal widths and distances optimally designed based on sensitivity analysis.
Among the three sensors, the outer two serve as AC heaters and the middle one
as a DC detector. The 2{\omega} voltage signals across the detector in each
three-sensor group are measured, and then the data are processed by the
proposed Intersection Method to derive the thermal conductivities along
directions of interest. The application of the detector's 2{\omega} instead of
the heater's 3{\omega} voltage signals eliminates the errors introduced by the
uncertainties of thermal resistance in superficial structures (metal layer,
insulation layer, interface, etc.). Meanwhile, by replacing the fitting
algorithm with the Intersection Method, the local optimum trap of multivariate
fitting is avoided. To verify the accuracy and reliability, four typical
monocrystalline semiconductors, i.e., Si, GaN, AlN, and {\beta -Ga _2 O _3},
are measured, and the results are consistent with the literature. This method
will provide a comprehensive and versatile solution for the thermal
conductivity measurements of solid materials.
