The results of investigations of the microstructure in the initial phase of a spark discharge in air in the 1.5 mm long gap between a tip and a plane are presented. Measurements show that, within 15 ns after breakdown, the channel is a set of a large number of microchannels, the current in the channel grows almost linearly up to 1 kA, and the electron concentration reaches the value of 2 • 10^19 cm^(−3). Kinetic processes in a separate microchannel were calculated based on the experimental data. It was found that the average electron temperature is in the range of 4-8 eV, the electric field is ~ 300 kV/cm, and the electrical conductivity is ∼10 Ω^(−1)•cm^(−1). The obtained results indicate that it is just the microstructure of the discharge determines the relatively high values of the average electron temperature in combination with a sufficiently high degree of ionization.