We experimentally study the transport properties of silicon quantum dots (QDs) fabricated from a highly doped n-type silicon-on-insulator wafer. Low noise electrical measurements using a low temperature complementary metal-oxide-semiconductor (LTCMOS) amplifier are performed at 4.2 K in liquid helium. Two series of Coulomb peaks are observed: long-period oscillations and fine structures, and both of them show clear source drain voltage dependence. We also observe two series of Coulomb diamonds having different periodicity. The obtained experimental results are well reproduced by a master equation analysis using a model of double QDs coupled in parallel. ; Comment: 5 pages, 4 figures, to appear in Jpn. J. Appl. Phys