A noncatalytic layer‐by‐layer self‐templated growth mechanism of carbon nanotube (CNTs) walls is presented. Growth occurs on both the inner and outer surfaces of the NTs. In both cases, the NT walls grow at the expense of disordered carbon or adatoms produced by electric breakdown (see image). The self‐templated growth results in thickening of the NT walls, reduction, or even disappearance of the NT hollow, and improvement of conductance. High‐temperature annealing improves the structure and electronic properties of CNTs.