I present deep spectroscopy of four H ii regions in the inner, metal-rich zone of the spiral galaxy M101 obtained with the LRIS spectrograph at the Keck telescope. From the analysis of the collisionally excited lines in two of the target H ii regions, H1013 and H493, I have obtained oxygen abundances 12 þ log (O/ H ) ¼ 8:52 and 12 þ log (O/H ) ¼ 8:74, respectively. These measurements extend the determination of the oxygen abundance gradient of M101 via the direct method to only 3 kpc from the center. The intensity of the C ii k4267 line in H1013 leads to a carbon abundance 12 þ log (C/ H ) ¼ 8:66, corresponding to nearly twice the solar value. From a comparison of the continuum temperature derived from the Balmer discontinuity, T (Bac) ¼ 5000 K, and the line temperature derived from [O iii] k4363/k5007, T ½O iii ¼ 7700 K, an average temperature T 0 ¼ 5500 K and a mean square temperature fluctuation t 2 ¼ 0:06 have been derived. Accounting for the spatial inhomogeneity in temperature raises the oxygen abundance obtained from the oxygen auroral lines to 12 þ log (O/H ) ¼ 8:93. These findings are discussed in the context of the calibration of strong-line metallicity indicators, in particular of the upper branch of R 23 . There is no evidence for the strong abundance biases arising from temperature gradients predicted theoretically for metal-rich H ii regions.