Nikon S6500 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor . On the other hand, Nikon S3500 has a
20.0MP 1/2.3-inch (6.16 x 4.62 mm ) sized CCD sensor .
Below you can see the S6500 and S3500 sensor size comparison.
Nikon S6500 and Nikon S3500 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.