Until Mansfield et al. developed a new immersion concept in 1990, termed the solid immersion lens (SIL),5 the main stream of research had focused on improving the performance of the objectives with liquid immersion and by finding better immersion liquids. The concept of solid immersion is derived from the idea that focusing in the center of a hemispherical solid leads to normal incidence of the rays with respect to the spherical interface, which is depicted in Fig. 1(d). In this way, one can avoid the refraction at the interface between the spherical solid and the surrounding medium (e.g., air). It leads to an increment of the NA by a factor of , the refractive index of the hemispherical solid medium [see Eq. (1)]. During the last two decades, numerous studies on SILs and their applications have been carried out. A majority of such studies focused on the macroscopic-size (i.e., millimeter scale) SILs due to the lack of fabrication technologies. Recent advances in micro- and nano-fabrication technologies enabled the development of different types of SILs, including diffractive SILs,6 micrometer-size SILs,7–10 nanoscale spherical lenses,11 and wavelength-scale SILs.12 In general, for structures smaller than the optical wavelength, design methods for larger devices, such as ray optics, are not applicable. More specifically, subwavelength-scale lenses cannot simply be considered refractive optical surfaces. However, recent experimental work has shown that subwavelength-scale SILs are still expected to produce a reduced-size focal spot,12 the so-called immersion effect. Recently, we reported the first experimental demonstration of the immersion effect in subwavelength-scale SILs.13 In fabrication, the ideal case leads to hemispherically shaped SILs. In reality, it is difficult to achieve the exact shape of the ideal design. In this study, we systematically investigate the light confinement effect of nonideally shaped SILs by using different shapes of nano-pillars. When an over-reflow occurs, the noncircular structures, such as square and triangular pillars, are easily transformed into spherical caps. However, in this case, the drawback is an enlarged size in the transverse directions. Thus, we look for the optimal reflow conditions to achieve a minimal expansion of the original size of the nano-pillars. The optical characterization of such small SILs has been realized by using a high-resolution interference microscope (HRIM). The HRIM facilitates complex alignment tasks by the in situ monitoring of the illumination beam. The aim of this paper is to report on the optimal reflow conditions for such small nano-pillars and the light confinement effect of nonspherical nano-SILs.