Direct Numerical Simulations (DNS) were carried out to investigate the laminar-turbulent transition process for a slender (2.5◦ half-angle) straight (right) cone at Mach 6 and zero angle of attack. The slender cone geometry of the experiments in the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University was used for the numerical investigations. The simulation results indicate that the so-called fundamental breakdown was the dominant nonlinear mechanism in the downstream part of the slender cone geometry where “hot” streaks have recently been observed in the BAM6QT experiments. Contours of the time-averaged Stanton number obtained from DNS also exhibited the formation of “hot” streaks similar to the ones detected in the experiments. The results for the slender cone provide additional evidence that the laminar turbulent transition process and the associated “hot” streak development for the “quiet” flow conditions in the BAM6QT facility is dominated by the fundamental breakdown mechanism.