Due to the dramatic downscaling of device features in recent technology nodes, characterizing the electrical properties of these structures is becoming ever more challenging as it often requires metrology able to probe local variations in dopant and carrier concentration with high accuracy. As no existing technique is able to meet all requirements, a correlative metrology approach is generally considered a solution. In this article, we study size-dependent effects on the dopant activation in nanometer-wide Si fins using a novel correlative approach. We start by showing that the micro four-point probe technique can be used to precisely measure the resistance of B doped and (laser) annealed Si fins. Next, we use transmission electron microscopy and scanning spreading resistance microscopy to show that the observed width dependence of the apparent sheet resistance of these fins can be explained by either a partially or a fully inactive region forming along the top of the fin sidewalls according to the annealing conditions.