In adult somatosensory cortex, only 10% of excitatory inputs to L4 cortical neurons are provided by thalamic inputs. The remaining 90% of synapses are of intracortical origin, largely representing recurrent excitatory connections between neighboring neurons within a single barrel which enables amplification of the thalamic inputs. Our aim was to characterize the development of excitatory connections between L4 neurons during the postnatal period. Using dual patch-clamp recordings from the neurons in slices of postnatal days (P4-15) rat somatosensory barrel cortex we analyzed 128 neuronal pairs at different ages. We found two types of connections between barrel cells during the postnatal development: (i) electrical connections and (ii) chemical glutamatergic synapses. These were identified on the basis of their electrical coupling and sensitivity to carbenoxolone. Electrical synapses were observed in 10-15% of recorded pairs during the first postnatal week, and their expression progressively decreased with age. Glutamatergic synapses showed an inverse developmental profile: no glutamatergic connections were detected until the postnatal age P5, and their incidence progressively increased with age, reaching nearly 25% probability of all pairs by the end of the second postnatal week. Thus, the development of connectivity between barrel neurons is characterized by a developmental switch from electrical to chemical connectivity and this transition coincides with a switch in sensory mode processing from bursting to acuity. We hypothesize that electrical synapses between barrel cells support their synchronization during generation of the early oscillatory activity patterns that are characteristic of the developing thalamocortical networks during the first postnatal week.